The invention relates to a connector assembly that is that is subjected to alternate loads by an axial flow of force between zero and various maximum values, and a method of forming same.
A connector assembly is known from DE 43 22 717 A1. By means of the assembly described in this document, in a three-part commercial vehicle frame consisting of front and rear cross members made of lightweight metal castings as well as a middle piece of a side member that connects the front cross members with the rear cross members, a permanent connection of the cross members with the middle piece of the side member composed of extrusion-molded sections made of lightweight metal is achieved. The assembly is formed by a sleeve-shaped connecting element that constitutes one assembly component, said element being inserted into the internal contour of a hollow section of the middle piece of the side member that constitutes the other assembly component, forming a connection that is secured by shape and force. At the other end, the connection element, provided there with an internal thread, is fastened for example by screwing to the respective cross member. The assembly is subjected to extremely high loads by alternating stresses in the axial direction, in other words tension and compression, as well as transverse loads during the driving of the commercial vehicle, so that in the course of the operating life, overloads on the connection can develop because of a lack of ability to expand or exceeding of stresses, especially in the area of the end of the connecting element located in the section, that lead to cracking of the section as the result of a sudden fatigue fracture. This fracture of the section cannot be detected in advance. The cracking of the section destroys the assembly, and the connecting element loses its supporting ability, whereupon the respective cross member comes free from the middle piece. As a result, unforeseeable accidental consequences can result, especially as a function of the cargo being carried during driving.
A goal of the invention is to improve a connector assembly such that failure of the assembly as the result of a fatigue fracture resulting from overload at the end pointing in the assembly direction can be detected in simple fashion in the functional assembly even before it occurs.
This and other goals have been achieved according to the present invention by providing a connector assembly, comprising: a hollow outer assembly component; and an inner assembly component arranged in the outer assembly component with an outer periphery of the inner assembly component adjacent an inner periphery of the outer assembly component over an axial distance; the inner assembly component being axially fixed relative to the outer assembly component along a portion of said axial distance defining a zero-play area, and the inner assembly component being axially movable relative to the outer assembly component along a portion of said axial distance defining an axial-play area, said zero-play area and said axial-play area axially abutting each other to define a desired fracture location.
This and other goals have been achieved according to the present invention by providing a method of forming a connector assembly having a hollow outer assembly component and an inner assembly component, said method comprising: arranging said inner assembly component in said outer assembly component with an outer periphery of the inner assembly component adjacent an inner periphery of the outer assembly component over an axial distance; axially fixing the inner assembly component relative to the outer assembly component along a portion of said axial distance in order to define a zero-play area; allowing the inner assembly component to be axially movable relative to the outer assembly component along a portion of said axial distance defining an axial-play area axially abutting said zero-play area, in order to define a desired fracture location between said zero-play area and said axial-play area.
According to the invention, the fatigue fracture of the assembly is displaced from the connecting end that points in the assembly direction to the other connecting end, with the breakage of one of the assembly components not immediately destroying the entire connection. Instead, a residual connection remains since the assembly components overlap one another over a reduced connecting length in a manner that produces a connection. The required strength for the connection with respect to additional axial alternating stresses, also with respect to overstresses, and hence sufficient carrying capacity of the connection, is ensured. This has the effect of extending the lifetime of the connector assembly, since the assembly, after the first fracture, fails completely only when, as a result of fatigue, a crack appears at the connecting end that points in the assembly direction. As a result of the displacement of the area that is subjected to the highest load, this area is, in essence, relieved of its load so that after the first fatigue fracture occurs between the connecting ends, the remaining structure will support a plurality of alternate stress cycles until a second fatigue fracture that is responsible for the final failure of the connection occurs at the connecting end that points in the assembly direction. The displacement of the fracture site occurs because, by providing an area that has play and another area immediately adjoining it with zero play, at the transition between the two areas there is less axial expandability than in the area of the assembly end pointing in the assembly direction and therefore any exceeding of stresses is displaced from this end of the connection to the transition. The assembly direction is the direction of the translational insertion movement of the inner assembly component into the outer assembly component when fitting the two assembly components together.
The first crack can be viewed, in essence, as a precursor for the later cracking of the connector assembly. The crack runs through the location of the specified breaking point between the connecting ends as a result of the abrupt increase in axial expandability of the connector assembly, in other words because of discontinuities in rigidity, immediately behind the point on the side of the assembly end locally defined in the transverse direction of the assembly. This point can be investigated, for example by inspection, in a simple fashion and at low cost to determine whether a crack has occurred there or not, in order to evaluate the loading capacity. When the first crack appears, which can be detected in simple fashion and is displaced locally, an intervention can be made accordingly by replacing the assembly component so that the connector assembly again has its full loading capacity. Serious consequential damage, especially when the connector assembly is used in frame parts of commercial vehicles, is thus avoided and the safety of the vehicle when driving is therefore increased.
According to the invention, failure of the connector assembly takes place in two stages that proceed clearly separately from one another in time and space, so that when the first crack occurs, but the connection can still provide support and therefore remains capable of accepting loads, a regular monitoring of the location can detect this before the connection finally fails. In this way, otherwise necessary expensive safety measures such as costly cable-type catching devices or stops can be avoided that are provided to protect against unforeseeable cracking at the end of the connection that points in the assembly direction.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.